As the issue editors Philip J. Boon and John M. Baxter outline, the pressures faced by aquatic ecosystems have largely intensified since the journal’s founding in 1991, and policy and management responses have developed in tandem. Pressures from urban development, hydropower, agriculture and industry have worsened across Europe in that time, whilst emerging topics such as climate change and ocean acidification, river basin management, ‘people and nature‘ conservation, ecosystem services and economics, conservation genetics and invasive alien species have become common aquatic research themes, often through new multidisciplinary approaches. A set of overarching European policies addressing aquatic environments have been set in the same period, including the Habitats Directive, Floods Directive, Water Framework Directive, Marine Strategy Framework Directive, and the EU Regulation on Invasive Alien Species.

So, what is the current state of play in aquatic conservation, and how might things change in coming years? The articles in the special issue address a range of topics in response to these questions.

Fish populations – both in freshwaters and in the sea – are chiefly threatened by habitat loss and degradation, invasive species, pollution and over-exploitation, as Angela Arthington and colleagues report, pressures which are all potentially intensified by climate change. Size matters, too: smaller fish are generally threatened by their habitats becoming increasingly isolated and fragmented; whereas larger species are most often threatened by over-fishing. The authors suggest that expanded conservation measures (such as protected areas) which ideally encompass both freshwater and marine environments and reduce human pressures on fish populations – particularly at migratory ‘bottlenecks’ such as estuaries – are needed to mitigate ongoing ecological damage.

Invertebrates are some of the most important, but under-studied and protected, organisms in aquatic ecosystems, according to Kevin Collier and colleagues. The authors report that global assessments of 7857 freshwater invertebrates and 2864 marine invertebrate species (of which a third were reported as lacking suitable data), the most threatened taxa were those with poor dispersal abilities and local endemism, for example many gastropods, crayfish and mussels. Invertebrate populations are richest in freshwater springs and subterranean hydrological systems, and in marine coral reefs and lagoons; but increasingly impacted by pollution, over-exploitation, habitat degradation and invasive species. The authors argue that to increase political and conservation engagement with aquatic invertebrates, work needs to be done on better understanding their global diversity and extinction threats.

Michael Gangloff and colleagues review a set of emerging threats to aquatic ecosystems – as in the previous papers, these are habitat loss and fragmentation, pollution, over-exploitation and invasive species and diseases – and suggest a range of potential mitigation strategies, ranging from more traditional legislation to newer nature-based solutions such as green infrastructure in cities for buffering pollutants. The global spread of one of these key threats – invasive species – is investigated by Elena Tricarico and colleagues, who examine data from three regions with different climates and ecological histories – temperateEurope,tropicalAsianHongKong,andNeotropicalBrazil. They find that freshwaters are more susceptible to invasion than marine habitats, but that (as for invertebrates in the Collier et al study) detailed and up-to-date nationalandregionalinventoriesofinvasive species presence and impact are lacking in many areas.

As Gangloff and colleagues outline, there are a range of management approaches used in mitigating stresses on aquatic ecosystems. One key approach is habitat restoration. In their paper, Juergen Geist and Stephen Hawkins demonstrate how restoration approaches are increasingly incorporating concepts from advancing ecological theory, such as the importance of (re)building ecosystem processes, connectivity and resilience. They suggest that a key balance to be struck in restoration is incorporating such concepts into adaptive management, whilst at the same time setting clear goals for the restored ecosystem’s trajectory, which are important for leveraging political and public support.

Wetlands are often a focus for restoration management as they are often hotspots for biodiversity, valuable natural filtration systems for pollutants, carbon sinks and flood buffers. However, the contribution by Richard Kingsford and colleagues suggests that wetlands remain ‘conservation’s poor cousins’ as whilst they cover between 5–10% of the world’s land surface, around 70% of wetland areas are highly damaged and degraded. As with reports on other aquatic ecosystems and species in this collection, Kingsford and colleagues report that the distribution and health of global wetland ecosystems is poorly mapped. As such, they suggest that wetland research should be prioritised by conservationists as many wetland ecosystems face increase pressures from water abstraction, draining and conversion into agricultural land across the world.

Three more papers consider the importance of human value systems in guiding aquatic conservation efforts. Kenneth Irvine and colleagues outline the challenges of conserving tropical aquatic ecosystems which are often highly biodiverse, yet data poor. They highlight the potential of applying the ecosystem service framework through local and national institutions to aim for sustainable human use of aquatic ecosystems, based on ongoing monitoring,reportingandaccountability of management.

Andrew Boulton and colleagues that the ecosystem service framework should be used to complement – rather than replace – existing conservation and restoration goals for biodiversity and ecosystem health. They outline four recommendations for setting ecosystem service-based goals for conservation:

explicitly listing and evaluating the sets of ecosystem services to be conserved;

identifying potential trade-offs arising from their conservation;

specifying time frames for ecosystem service conservation (or enhancement); and

forecasting how conservation strategies might benefit ecosystem function, service flow and public benefit.

What is The Freshwater Blog?

Features, interviews and analyses on freshwater conservation, science and policy.

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The blog was founded and edited between 2010-14 by the BioFresh project, an EU-funded project that built a global information platform for scientists and ecosystem managers with access to all available data describing the distribution, status and trends of global freshwater biodiversity.

Since 2014, the blog has been managed and edited by the MARS project – an EU-funded project which investigates how multiple stressors affect rivers, lakes and estuaries.

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